The present invention relates generally to Internet Protocol (IP) multimedia services and, more particularly, to maintaining an IP Multimedia Core Network Subsystem (IMS) registration while a user equipment (UE) is disconnected from an IP bearer.
IMS is a standardized architecture for network operators and service providers that wish to provide mobile and fixed IP multimedia services to customers irrespective of the customers' location, access technology, and user equipment. IMS runs over standard IP, and provides network operators and service providers the ability to control and charge for individual IMS-based services, and allows customers to execute services both in home and roaming networks. These IMS-based services can use the same protocols as existing Internet services, and may comprise for example: presence, messaging, push to talk (PTT), and telephony.
In order to maintain access to the IMS services, it is mandatory for the UE to keep the IP connectivity access network (IP-CAN) bearer established, and many IMS services can be expected to be continually accessed for a long duration, such as hours or days. On some IMS services the UE is expected to be “always-on”, available from power up until power down. Consider for example a presence service in which the UE automatically registers into an IMS presence service upon power up. The associated user then becomes online for all the other IMS users who subscribed and are authorized to see the user's presence. The user should then stay online for as long as the UE is powered up. This presence service requires the UE to register in the IMS and remain registered in the IMS for as long as the UE is powered up. Similarly, in an always-on IM or PTT IMS service, the user expects to be able to be contacted by IM or voice by his contacts at any time once the UE is powered up. This again requires the UE to register in the IMS and remain registered in the IMS for as long as the UE is powered up.
In order for these IMS services to function, the UE needs to maintain IP connectivity through the IP-CAN bearer. Otherwise, the UE must de-register or be de-registered from the IMS, thereby stopping the IMS services. Maintenance of a wireless IP-CAN bearer for a long duration, such as hours or days, can be expensive and difficult, if not impossible.
For financial reasons, most mobile network operators deploy their high-speed IP-CAN infrastructure such as Universal Mobile Telecommunications System (UMTS) in a gradual manner. Initially, coverage is spotty, and increases as capacity is built up. Some mobile network operators will provide access to IMS services via only their high-speed IP-CAN infrastructure, though they may implement mitigation strategies to increase their IMS coverage. For instance, they may deploy UE's supporting high-speed access to IMS services in areas where such high-speed access is deployed, but also supporting IMS access through legacy wireless data communication technologies such as GPRS or CDMA in areas where high-speed IMS access technology is not deployed. Nonetheless, an IMS UE may not be able to maintain the IP-CAN bearer in the case that IMS services are only available through high-speed IP-CAN infrastructure while the coverage is spotty. Alternatively, if the IMS UE maintains IMS access when outside the coverage of the high-speed IP-CAN infrastructure by reverting to legacy technology such as GPRS or CDMA, this requires the IMS UE to establish an IP-CAN bearer over the legacy technology, and then to re-register in IMS over this latter IP-CAN bearer. As the IMS UE moves inside and outside of coverage of the high-speed IP-CAN infrastructure, the IMS UE must then constantly re-establish its IP-CAN bearer with the high-speed IP-CAN infrastructure or the legacy infrastructure, and re-register into IMS. These constant re-establishments of IP-CAN bearers and registrations into IMS impose increased signaling traffic on the UE, the mobile network, and the IMS, thus imposing increased costs.
The requirement to maintain the IP-CAN bearer also imposes constraints on the UE and network resources. The need for the UE to maintain IP connectivity through the IP-CAN bearer can particularly become a stringent constraint if the UE is accessing IMS services through legacy technologies such as GPRS or CDMA. Maintaining long-lived IP connections through such legacy technologies can severely tax both the user equipment (e.g., battery life can be shortened) as well as the network resources (e.g., in GPRS a large number of Packet Data Protocol (PDP) contexts may need to be maintained active concurrently).
For the foregoing reasons, there is a need to enable an IMS UE to maintain its registration in its IMS services even while the UE is disconnected from an IP bearer.